Comparison of flexural strength, marginal gap, and internal fit of milled and 3D-printed crown materials

The purpose of this study was to compare the flexural strength, Weibull modulus (reliability), marginal gap, and internal fit (internal gap) of 4 materials for milling or 3-dimensional (3D) printing of definitive and provisional crowns: IPS e.max CAD (IEC), Paradigm MZ100 Block (PMB), Permanent Crown Resin (PCR), and Temporary CB Resin (TCR). Flexural strength was tested by subjecting sectioned milling blocks (IEC and PMB) or 3D-printed bars (PCR and TCR) to a 3-point bending test in a universal testing machine (n = 15 per material). Crowns were milled or 3D printed, and the marginal gap and internal fit were measured using microcomputed tomography (n = 5 per material). The data were analyzed with a t test and compared using analysis of variance (ANOVA) with Tukey post hoc comparisons (α = 0.05). The groups demonstrated the following mean (SD) flexural strength values: IEC, 335.50 (28.97) MPa; PMB, 154.34 (21.03) MPa; PCR, 128.09 (7.30) MPa; and TCR, 126.29 (9.23) MPa. A 1-way ANOVA revealed significant differences in the flexural strengths of sectioned and 3D-printed bars (P < 0.001). The PMB group showed the lowest Weibull modulus (8.77), indicating its poor reliability. The IEC group showed the smallest marginal gap, 53.42 (31.99) μm; this value was significantly smaller than the gap in the TCR group (P < 0.001) but not the PCR or PMB group. The PMB group had the smallest internal fit discrepancy (87.44 [37.60] μm) but was not significantly different from PCR, while TCR had a significantly greater internal fit discrepancy (130.61 [65.16] μm) than IEC, PMB, and PCR (P < 0.001). The occlusal internal fit discrepancies of 3D-printed crowns were significantly greater than those of milled crowns (P < 0.001). There was no statistically significant difference in flexural strength between the 3D-printed definitive (PCR) and provisional (TCR) materials. When the data were combined according to manufacturing method, the marginal gap and internal fit of crowns fabricated with 3D printing were comparable to those of milled crowns, and all mean marginal gaps were within a clinically acceptable limit of less than 120 μm.